That's about three cups per coffee drinker in the United States, where 83 percent of adults can't imagine life without their favorite cup of java.

Add to that tea, caffeinated soft drinks and those infamous energy drinks, and you won't be surprised to read that 90 percent of us consume caffeine in some form or another each day. Is this a bad thing? Not entirely.

Recent research has shown that coffee, in particular, may help prevent diseases like stroke and certain cancers, lower our risk of Parkinson's and dementia, and boost our concentration and memory. Partly that's because coffee beans are seeds, the National Institutes of Health (NIH) reminds us, and like all seeds, they're loaded with protective compounds.

"Coffee is an amazingly potent collection of biologically active compounds," Walter Willett, M.D., of the Harvard School of Public Health, told the National Institutes of Health's newsletter.

Caffeine, a mild stimulant, also provides benefits: It's been linked to lower risks of Alzheimer's disease, for example. But when it comes to caffeine, there really can be too much of a good thing. Those who study caffeine's lesser-known effects point to studies that indicate it can be worrisome for people with high blood pressure, diabetes and osteoporosis. Plus, caffeine can interact poorly with some common medications, and it can worsen insomnia, anxiety and heartburn.

It would make things easier if the caffeine content were listed on food labels so you would know if you've exceeded the 300 mg level that most health experts say is a safe, moderate amount for the day — about the amount in three 8-ounce cups of coffee, depending on how strong you brew it — but so far that's not happening.

So before you turn on that coffeemaker or grab a grande cup from your favorite cafe, here are some things to keep in mind.

First, the bad news about caffeine (and coffee)

Remember: Caffeine is a drug, says Steven Meredith, a researcher in behavioral pharmacology at the Johns Hopkins School of Medicine.

While low to moderate doses are generally safe, caffeine is addictive and users can become dependent on it and find it difficult to quit or even cut back, he says. (Caffeine dependence was even named as a new mental disorder this year.) Anyone who's ever quit cold turkey knows it can trigger pounding headaches, mental fuzziness and fatigue for a couple of days until the body adjusts.

Other effects of too much caffeine:

It increases anxiety and disrupts sleep patterns, leading to a vicious cycle of restless sleep, relying on caffeine to help with daytime fatigue, followed by more insomnia.

It increases blood sugar levels, making it harder for those with type 2 diabetes to manage their insulin, according to a number of studies; it also can slightly raise blood pressure. If you have difficulty controlling either your blood pressure or diabetes, switching to decaf may help, says Rob van Dam with Harvard's School of Public Health.

Caffeine Counts

The amount of caffeine in a particular coffee drink depends on the brew and beverage size:

Restaurant espresso (1 oz.) 40-75 mg

Instant coffee (8 oz.) 27-173 mg

Typical brewed coffee (8 oz.) 95-200 mg

McDonald's brewed coffee (16 oz.) 100 mg

Starbucks brewed coffee (16 oz.) 330 mg

Source: Mayo Clinic

Caffeine potentially leads to some spinal bone loss in postmenopausal women if they typically drink more than three cups, or 300 mg of caffeine, a day, but don't get enough calcium in their diet, says Linda Massey, emeritus professor of nutrition at Washington State University. An older woman should make sure she gets at least 800 mg of calcium daily — through food or supplements — to offset caffeine's effect on calcium, adds Bess Dawson-Hughes, M.D., director of the Bone Metabolism Laboratory at Tufts University in Boston.

Coffee itself can also mess with your stomach. If you have problems with acid reflux or heartburn, then coffee and even tea might not be right for you.

And if you have high cholesterol and you don't want your coffee adding to the problem, you need to use a paper filter to trap the cafestol, a compound in coffee that raises LDL cholesterol levels, says van Dam.

Here's what you need to know if you have a touchy tummy

Coffee's not your friend if you're prone to heartburn. Coffee is highly acidic and is irritating to the gastrointestinal tract. Switching to decaf won't help: In fact some research has found that decaf increases stomach acid even more than caffeinated coffee. Neither will switching methods of brewing or roasting. Avoiding coffee is the only solution.

Caffeine's not your friend if you have acid reflux. Caffeine seems to be the main culprit by relaxing the sphincter muscle that normally keeps stomach acid from bubbling up the esophagus. Decaf coffee has significantly less of a reflux effect, studies have found.

Now, the good news about caffeine (and, of course, coffee)

Caffeine has been shown to protect against a host of problems. Some studies have found that those who drink lots of coffee (but not decaf) seem to be four to eight times less likely to develop Parkinson's disease, according to the NIH's National Institute of Neurological Disorders and Stroke, and "that is more likely to be due to caffeine" than to any nutrients in coffee, says van Dam.

Some other benefits of coffee:

It may reduce the risk of Alzheimer's and dementia. A caffeine habit in your 40s and 50s — three to five cups daily of the high-octane stuff, not decaf — seems to reduce by up to 70 percent the risk of Alzheimer's and dementia in your 70s, a 2009 University of Florida study found. Other studies have found that regular caffeine consumption may help slow the rate of cognitive decline in older adults.

Coffee cuts suicide risk. A 2013 study by Harvard's School of Public Health found that those who drank two to three cups of caffeinated coffee a day cut their suicide risk by 45 percent — possibly because caffeine's stimulant effect helps boost people's moods.

Related

It lowers the risk of oral cancers. Older adults who drank four or more 8-ounce cups of regular coffee daily were half as likely to die of mouth and upper throat cancer. Decaf had a weaker effect, while no protection was found with tea.

Coffee lowers the risk of stroke for older women. A 2009 U.S. study and a 2011 Swedish study both found that older women who drink more than a cup of caffeinated coffee daily have a 20 to 25 percent lower risk of stroke. A 2008 Swedish study found a similar result in older men.

Caffeine aside, coffee can be considered a healthy drink, judging by the preponderance of research suggesting it may protect against a variety of diseases and help us live longer. Keep in mind that these studies found an association between better health and coffee drinking, but researchers haven't yet found exactly what causes these benefits. It could be, for example, that coffee drinkers are more active and social. Or it could be that one of the more than 1,000 compounds that coffee naturally contains boosts our health. We don't know.

Some of the benefits you might be getting from your favorite cup of joe

A longer life. The largest study to date, a joint project last year by the NIH's National Cancer Institute and AARP that followed 400,000 men and women ages 50 to 71 for more than 10 years, found that those who regularly drank coffee — either decaf or regular — had a lower risk of overall death than did nondrinkers. In particular, the coffee drinkers were less likely to die from heart disease, respiratory disease, stroke, injuries and accidents, diabetes, and infections.

Protection against a number of cancers. A 2010 overview of major studies on coffee consumption and cancer by the University of California, Los Angeles, found a strong protective association between coffee and endometrial (also called uterine) cancer and some protection from colon cancer; other recent studies have found that drinking coffee may protect against prostate and liver cancer.

Reduced risk of type 2 diabetes. "Studies from around the world consistently show that high consumption of caffeinated or decaffeinated coffee is associated with low risk of type 2 diabetes," says Harvard's van Dam. That's true even though coffee may raise blood glucose levels in people with diabetes, at least on a short-term basis. His recommendation: Switch to decaf because some research shows it has less of an effect on blood sugar.

Bottom line: It's all about you. People have different reactions to caffeine. Some can drink six cups of coffee a day and feel fine, others need to switch to decaf or herbal tea by noon or they'll be up all night.

If you need to cut back on your caffeine consumption, do it slowly over several weeks, gradually adding more decaf to your regular brew. And don't forget: That big cup of soda and your favorite chocolate bar also contain caffeine.